The present invention relates to substantive Ultraviolet (UV) radiation-absorbing compounds, and more particularly to water-soluble and water-dispersible cationic UV-absorbing compounds demonstrating a superior level of substantivity.
UV-absorbing compounds have found wide use in compositions such as sunscreens, tanning lotions and the like, as protective agents against sunburn or erythema. The utility of UV-absorbing compounds derive from their strong absorption of energy in the UV region of the spectrum.
Solar UV radiation having a wavelength of 290-313.mu. is known to produce erythema, particularly in fair-skinned individuals. Solar UV radiation of from 315-320.mu. to 350-400.mu., on the other hand, promotes a tanning of the skin. Therefore, sunscreen and tanning compositions are preferred that remove substantially all of the burning rays, while transmitting the tanning rays. Accordingly, UV-absorbing compounds for use in such compositions must absorb at UV wavelengths known to produce erythema and at the same time absorb relatively little energy in the region of the UV spectrum known to produce skin tanning.
Commonly used UV-absorbing compounds include salicylic acid, p-aminobenzoic acid (PABA), 2-hydroxybenzophenone, 2-hydroxybenzotriazole, cinnamic acid, derivatives thereof, and the like. One drawback to these compounds is their low level of adhesion to the skin, which, in combination with high water solubility, results in their being diluted by perspiration. Constant reapplication is particularly necessary when compositions containing these compounds are used in connection with swimming activities. The failure to protect because of lack of water-resistance has remained a primary source of dissatisfaction with sunscreen products containing UV-absorbing compounds.
In the past, product formulators attempted to impart a degree of water-resistance or substantivity to compositions containing UV-absorbing compounds by formulating the compounds with water-resistant or substantive carriers. Thus, sunscreen compositions were prepared based on hydrophobic vehicles. This was undesirable for several reasons. First, the water-soluble UV-absorbing compound upon exposure to sufficient moisture would eventually be extracted, or "leached" from the water-resistant carrier. In addition, the use of such hydrophobic carriers results in a product having an undesirable oily, greasy "feel."
U.S. Pat. No. 3,879,443 discloses substantive UV-absorbing compounds in which a hydroxylamine ester of a UV-absorbing carboxylic acid is reacted with a second UV-absorbing carboxylic acid to form an acid addition salt between the amine and the second acid. U.S. Pat. No. 4,256,664 discloses cationic salicylamido amine fatty quaternary salts having enhanced skin adhesion. Nevertheless, there remains a need for UV-absorbing compounds possessing improved skin adhesion in combination with water solubility, so that a substantive product may be provided free of a greasy, oily "feel."